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<a name="Argument-list-functions"></a>
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<a name="Argument-list-functions-_0025VAL_002c-_0025REF-and-_0025LOC"></a>
<h4 class="subsection">5.1.20 Argument list functions <code>%VAL</code>, <code>%REF</code> and <code>%LOC</code></h4>
<a name="index-argument-list-functions"></a>
<a name="index-_0025VAL"></a>
<a name="index-_0025REF"></a>
<a name="index-_0025LOC"></a>

<p>GNU Fortran supports argument list functions <code>%VAL</code>, <code>%REF</code>
and <code>%LOC</code> statements, for backward compatibility with g77.
It is recommended that these should be used only for code that is
accessing facilities outside of GNU Fortran, such as operating system
or windowing facilities.  It is best to constrain such uses to isolated
portions of a program&ndash;portions that deal specifically and exclusively
with low-level, system-dependent facilities.  Such portions might well
provide a portable interface for use by the program as a whole, but are
themselves not portable, and should be thoroughly tested each time they
are rebuilt using a new compiler or version of a compiler.
</p>
<p><code>%VAL</code> passes a scalar argument by value, <code>%REF</code> passes it by
reference and <code>%LOC</code> passes its memory location.  Since gfortran
already passes scalar arguments by reference, <code>%REF</code> is in effect
a do-nothing.  <code>%LOC</code> has the same effect as a Fortran pointer.
</p>
<p>An example of passing an argument by value to a C subroutine foo.:
</p><div class="smallexample">
<pre class="smallexample">C
C prototype      void foo_ (float x);
C
      external foo
      real*4 x
      x = 3.14159
      call foo (%VAL (x))
      end
</pre></div>

<p>For details refer to the g77 manual
<a href="https://gcc.gnu.org/onlinedocs/gcc-3.4.6/g77/index.html#Top">https://gcc.gnu.org/onlinedocs/gcc-3.4.6/g77/index.html#Top</a>.
</p>
<p>Also, <code>c_by_val.f</code> and its partner <code>c_by_val.c</code> of the
GNU Fortran testsuite are worth a look.
</p>



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